1. Field of the Invention
The present invention relates to an image processing apparatus capable of displaying an image for the left eye and an image for the right eye stereoscopically on a display unit, and a control method thereof.
2. Description of the Related Art
Japanese Patent Application Laid-Open No. 03-126377 discusses a technique for preferably correcting a gradation of a display image by setting a gradation correction parameter (γ curve) for each frame based on an amount of characteristics such as an average luminance level (APL) of a frame or a luminance histogram. The gradation correction processing is expressed as dynamic γ processing below.
Currently, a stereoscopic system has been known to stereoscopically display a three-dimensional (3D) video image including a left-eye video image and a right-eye video image using binocular parallax on a two-dimensional display screen. However, as a result of dynamic γ processing for each frame of a pair of an image for the left eye and an image for the right eye capable of stereoscopic display, if a large difference is generated between a gradation of the image for the left eye and a gradation of the image for the right eye, the stereoscopic display becomes difficult or a feeling of fatigue for the eyes increases.
Therefore, as a correction method for suppressing the increase in difference between the image for the left eye and the image for the right eye, Japanese Patent Application Laid-Open No. 2005-159755 discusses a technique for setting a γ curve based on an image of a common region between the image for the left eye and the image for the right eye and applying the γ curve to the image for the left eye and the image for the right eye. Further, Japanese Patent Application Laid-Open No. 2007-151125 discusses a technique for correcting the image for the left eye and the image for the right eye based on an average value of characteristics such as the luminances of the image for the left eye and the image for the right eye.
Since an image for the left eye and an image for the right eye in the 3D image are originally images in different viewpoints, even in the case of an image in the common region between the image for the left eye and the image for the right eye, the image for the left eye is slightly different from the image for the right eye. However, Japanese Patent Application Laid-Open No. 2005-159755 does not specifically describe from which one of the image for the left eye and the image for the right eye in the common region the γ curve is set, and how the γ curve is set by using the image in the common region between the image for the left eye and the image for the right eye.
Further, Japanese Patent Application Laid-Open No. 2007-151125 does not specifically describe what is the average value of characteristics such as the luminances of the image for the left eye and the image for the right eye. The average value of the luminances of the image for the left eye and the image for the right eye is calculated using the luminances of the image for the left eye and the image for the right eye, and the image for the left eye and the image for the right eye are corrected using the γ curve generated based on the gradation of the average value. In this case, a region with the luminance near the average value is properly corrected in the image for the left eye and the image for the right eye. However, a region with the luminance other than the average value cannot be properly corrected. When a specific region with a luminance value larger than the average value is included only in the image for the right eye, a large number of gradations are assigned to the gradation of the average value in the γ curve and a large number of gradations are not assigned to the gradation value of the luminance in the specific region, so that the correction cannot be properly performed.